The present invention relates to a photographic printer of the type in which printing magnification is variable and, more particularly to a photographic printer in which no focus-adjustment of an optical system of a scanner is required when printing magnification is varied.
There are various sizes of photographic films such as 35 mm size films, Brownie films, 110-size films and so forth, some of which can be used in full and half size. For making prints from these different sizes of films, a photographic printer is generally adapted to vary its printing magnification by changing a conjugate length of its printing lens.
Meanwhile, recent photographic printers have an exposure control system including an optical scanner comprising an optical system and an image sensor for detecting densities of a great number of points of an image recorded on the film. Based on the detected densities, image characteristic values are obtained so as to perform an exposure control with a high accuracy. Since the scanner is generally so disposed as to have its optical axis inclined with respect to the printing optical axis, the image sensor receives a distorted image on its image receiving surface. This image distortion can be corrected by the provision of a reflection mirror removably disposed, or otherwise a half mirror fixedly disposed, in the printing optical axis in order to turn and direct at a right angle an image of the film to the image sensor.
In the case of the above described scanner incorporated in the photographic printer in which the conjugate length of printing lens can be varied to change its printing magnification, the optical system of the scanner can not focus a sharp image on the image sensor when printing magnification is changed. For this reason, the focus of the optical system of the scanner is to be readjusted every time the printing magnification is changed.